This invention relates to a silver halide photographic material, more particularly to a silver halide photographic material having not only improved keeping quality but also high sensitivity.
Silver halide crystals incorporated in silver halide emulsion layers for use in silver halide photographic materials are predominantly of normal (regular) shape.
Normal silver halide crystals have the advantage that they can be produced consistently and that desired shapes can be obtained. They also have high pressure resistance. Further, they permit the grain size to be controlled easily, thus contributing to ease in designing suitable photographic materials. Another advantage of normal silver halide crystals Is that the grain structures can be controlled easily. If, for example, a core/shell structure is to be formed, its composition can be easily controlled to provide a core of high iodine content and, at the same time, the thickness of the shell can also be controlled easily. Thus, normal silver halide crystals offer great benefits with respect to sensitivity and granularity.
In spite of these many advantages, normal crystals have a serious disadvantage in that their sensitivity has rather low aging stability. This problem is particularly great in normal crystals having (III) faces.
A method commonly employed to improve the aging stability of normal crystals is to increase the iodine content of their surface. This technique is effective in preventing the decrease in sensitivity with time but, on the other hand, the sensitivity of fresh samples (before aging) decreases and in addition, the improvement in keeping quality is unsatisfactory.
Normal crystal grains has the additional problem that their ability to adsorb dyes is generally weak and thus fail to provide a desired increase in sensitivity by treatment with spectral sensitizing dyes.